Acoustical velocity well logging



Jan. 14, 1964 K. D. SAVAGE 3,118,127

AcoUsTIcAL VELOCITY WELL LoGGING Filed sept. 28, 1959 4 sheets-sheet 1 Jan. 14, 1964 K. D. SAVAGE ACOUSTICAL VELOCITY WELL LOGGING 4 Sheets-Sheet 2 Filed Sept. 28, 1959 6e/referer 45' G Jan. 14, 1964 K, D. SAVAGE 3,118,127

AcousTIcAL VELOCITY WELL LoGGING Filed sept. 28, 1959 4 sheets-sheet s 'to t mgas/fr A# M5 imm/L --T- Jan. 14, 1964 K, D SAVAGE 3,118,127

ACOUSTICAL VELOCITY WELL. LOGGING United States Patent 3,118,127 ACUSHCAL VELCHTY WELL LGGGNG Kerry D. Savage, Houston, Tex., assigner to Texaco Enc., New York, NX., a corporation of Delaware Filed Sept. Z8, 1959, Ser. No. 843,002 14 Claims. (Cl. 349-18) This invention relates to the determination of the nature of subsurface strata, and, more particularly, to a determination of the acoustical properties of subsurface strata which has been traversed by a borehole.

In acoustical velocity well logging, as it is generally practiced today, the velocity of an ultrasonic wave through the various subsurface formations is determined by producing an acoustic pulse at a repetition rate of about 2O times a second, however, repetition rates of from l() to 40` times a second have been found acceptable, and determining the lapse of time of one of the acoustic pulses travelling through the subsurface formation between two spaced apart points in the borehole.

In the prior art acoustical velocity logging systems, a separate electrical channel has been provided between the first point of the two spaced apart points and an elapsed time measuring circuit and a separate electrical channel has been provided between the second point and the measuring circuit. lIn some instances, the tw-o electrical channels coupled to the measuring circuit have been terminated in the borehole, for example, as disclosed in in the ccpending U.S. patent application of R. H. Loofbourrow having Serial No. 574,844, now Patent No. 2,931,455, and entitled Acoustic Logging of Wells, and in other instances the channels have been extended up through the borehole Ivia a multi-conductor cable to the measuring circuit disposed at the surface of the earth. In addition to providing at least two electrical channels for Iapplying signals from -the two spaced apart points to the measuring circuit, another channel has been provided for applying an electric pulse to a transmitting transducer to produce the acoustic pulses in the borehole and an additional channel has been provided to energize the downhole or exploring unit electronic equipment, thus necessitating the use of at least :a four conductor cable. In the instances where the channels between the two spacd apart points and the measuring circuit of acoustical systems have been confined entirely within an exploring unit or tool located in the borehole, it has been found that it is diiiicult, if not impossible, to properly calibrate these systems. These latter systems transmit an electrical signal through the borehole which is intended to be an indication of the velocity of the subsurface formation adjacent the exploring unit but this signal has been found to be dependent upon unknown conditions in the unfriendly environment of the borehole.

yIn accordance with the present invention, an improved acoustical velocity well logging system has been provided wherein an exploring unit having at least two transducers is disposed in the borehole while the elapsed time measuring circuit is disposed at the surface of the earth and is coupled theretoby means of a single insulated conductor cable.

For a better understanding of the invention, reference may be had to the accompanying drawing in which FIG. 1 is a circuit diagram partly in block form illustrating the borehole equipment in accordance with the present invention, including a sectional View of a portion of the earths surface with part of the apparatus disposed in a borehole therein.

IFIG. 2 is a circuit diagram partly in block form illustrating the surface equipment of the ysystem of the present invention, including a sectional view of a portion of the earths surface wtih part of the apparatus disposed in a borehole therein.

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FIG. 3 is` a time sequence diagram of the voltages developed in the system of the present invention, and

FIG. 4 is an embodiment of a cable pulsing circuit which may be used in the borehole equipment illustrated in iFIG. l.

Referring in more detail to IFIG. 1 of the drawing, a borehole lf? containing a borehole liquid, which may be any convenientionally used bore hole drilling, mud, is shown traversing a plurality of subsurface formations 12, 14, and 16, in which formation it is desired to determine the acoustical velocity. Disposed within the borehole is an exploring unit or elongated tool 18 supported by a conventional 5/16 single insulated conductor borehole cable 20. The single conductor cable Ztl includes a central conductor 22, generally composed of copper, or other highly conductive metal, and an outer sheath 24 made of steel strands having a strength sufficient to support the exploring unit 18 and its own weight in the borehole. The exploring unit 18 has an acoustical section 26 at the lower end thereof in which an acoustic pulse transmitting transducer 28, a first acoustic pulse receiving transducer 30, and a second acoustic pulse receiving transducer 32 are contained. The transmitting transducer 28 and the first receiving transducer 30' are spaced apart a distance of, preferably, three feet and the first and second receiving transducers are spaced apart a distance of, preferably, one foot. Each of the transducers is, preferably, of the lead zirconate titanate type or of the barium titanate type. The walls and Ithe interior of the acoustical section 26 o-f the exploring unit #18 are made of a material in which velocity of sound is not greater than the velocity of sound passing through the fluid in the borehole 10, preferably, a material in which velocities are less than 5,000 feet per second and which can withstand the high temperatures and pressures encountered in a borehole, fore example, a rubber-like material such as neoprene. The upper portion of the exploring unit 18 is an electronic section 34 wherein the exploring unit electronic components are housed.

The electronic section 34 houses a timer unit 36 which may be any desirable oscillator producing pulses, preferably, at a constant repetition rate or frequency, for example, at 2i) pulses per second. An `acoustic transmitter pulser 38, which may be a conventional circuit for producing a sharp high energy electric pulse, is coupled to the output of the timer unit 36 and is connected at its output to the transmitting transducer 28. Also connected to the `output of the timer unit 36 is a first pulse delay unit e@ which may comprise a one-shot multivibrator and `a diflerentiator. A first gate generator 42, which may be a one-shot multivibrator, producing a positive square wave at its output is connected to the output of the first delay pulse unit 49. The first gate generator 42 is connected at its output to a grid of a first ldual control coincidence thyratron 44 of a first trigger generator 45.

The first receiving transducer 30 of the yacoustical section 26 of the exploring unit 18 is coupled to a first high-pass filter 46 which, preferably, has a cut-off frequency of approximately 5 kilocycles. A conventional first amplifier and clipper 48 is connected to the output of the first filter 46. The output from the first amplifier' and clipper 43 is applied to another grid of the dual control coincidence thyratron 44.

The anode of the thyratron 44 is connected to a B-lsupply of energy through ya charge resistor Si! Ihaving ya high resistance value. A storage capacitor 52 is connected between the anode of the thyratron 44 and ground. The shield grid of thyratron 44 is also connected to ground. A cathode resistor S4 is connected between the cathode of thyratron 44- and ground. A dual cathode follower 55 having la first triode section 53 and a second triode section fl has a common cathode resistor 62. The control grid of lthe lirst triode seotion 58 is connected to output l of the first trigger generator 45 which is the cathode of the thyratron 44 through a rst coupling capacitor 64. The control grid of the first triode section 53 is connected to ground through a iirst resistor 65 and a second resistor 67 is connected between the control grid of the second triode section 6G and ground.

A second pulse delay unit 7) which also may include a one-shot multivibrator and `a. dilterentiator is connected to output H of the first trigger generator which is a tap on the cathode resistor 54 of the thyratron 44. The output of the second pulse delay unit 7) is coupled to a second gate generator 72 which may Aalso comprise a oneshot multivibrator. The output of the second gate generator 72 is coupled to a first control grid of a second dual control coincidence thyratron 74 of a second trigger generator 75. A high resistor 76 is connected between the anode of the second hydrogen thyratron 74 and the B-lsupply. A capacitor 78 is connected between the anode of the second thyratron '74 and ground. The shield grid of the second thyratron 74 is also connected to ground. A cathode resistor 80 is connected between the cathode of the second thyratrcn and ground.

Coupled to the output of the second receiving transducer 32 is a second lilter 52 which is also, preferably, a high-pass filter having a cutoil frequency at approximately kilocycles. A conventionm second amplifier and clipper Se is connected to the output of the second lter 82. The output ot the second amplifier and clipper 84 is connected to a second control grid of the 4dual control coincidence thyrati'on 74. The cathode of the second ythyratron 74 is connected to the control grid of the second triode section 69 of the dual cathode follower Se.

The `cathodes of the dual cathode follower 56 are connected 'to a cable pulsing circuit 87 and, more particularly, to the control grid of a hydrogen thyratron 3S of the cable pulsing circuit 87 through a coupling capacitor 90. The control grid ot` the hydrogen thyratron S8 is also connected to a negative direct current potential through a choite 2. An energy storing or pulse forming network 94, which includes rst and second capacitors 96 a id 98 and a coil i60, is connected -at one terminal to ground and at the other terminal directly to the anode of the hydrogen thyratron 38 and through a resistor lil?. to the B+ supply. ri`he energy sto-ring network 94 may conveniently be a predetermined length of coaxial cab-le. A ycathode resistor lll@ having a low ohmic value is connected between the cathode or" the hydrogen thyratrori S3 and ground. A coupling capacitor lilo is connected between the cathode of the hydrogen thyratron 5S and the single conductor cable 20. A borehole power supply lt is connected .to the single conductor 22 of the single conductor cable 2li) through a iilter network 110 which includes a capacitor liz connected between the input of the borehole power supply 1%?8 and ground and an inductor 114iwhich is connected between the input of the borehole power supply ll `and the single conductor 22 of the single conductor cable 2G.

The surface equipment of the acoustical velocity well logging system of the present invention is illustrated in FlG. 2. As shown in this ligure, the single conductor cable 26 passes o-ver a cable measuring device M6. The upper or surface end of the single conductor 22 of the single conductor cable 2li is connected to a first primary winding lt of a step-up transformer 120, the sheath 24 of the cable 2@ being connected to ground. A sec-ond primary windinU 1.22 of the :transformer 120 is serially connected with the first primary winding 113 and also 'with Ian inductor 12.4 to the output of a power supply 125 which is, essentially, a variable step-up transformer, increasing the ll() volts, 60 cps. of a power source 125 to approximately 280 volts, 60 c.p.s. A surface power supply 123 is also `connected to the output of the ll() volts, 60 c.p.s. power source i253. A lirst capacitor is connected between the output of the power supply 125 and ground. A second capacitor 132 is connected between the output of the power supply 126 and the common point between the first and second primaly windings 118, 122 of the transformer lZtl. A secondary winding 134 of the transformer 129 is connected to a high-pass filter 136. The output from the high pass filter 136 is connected to a conventional amplifier 138 which has its `output connected to a blocking oscillator 146.

The output of the blocking oscillator 146` is connected to the control grid of a cathode follower 17). The anode of the cathode follower 170 is connected directly to the B-lsupply, the cathode of the cathode follower i170 is connected through a load resistor 172 to ground and the control grid is connected to ground through a grid resistor 16S.

The cathode of the cathode follower 170` is connected to a scale-of-two circuit 174 which is in turn connected to a sawtooth generator 176, the scale-of-two circuit being, preferably, of the type described in Electronics, by Elmore and Sands, page lll, published by McGraw-Hill, first edition. A peak reading vacuum tube voltmeter 178 is connected to the output of the sawtooth generator 176. A direct current voltage amplifier couples the pealt reading vacuum tube voltmeter 178 to a recorder 1552. rllhe recorder 182 may include any conventional recording medium, such as a chart, film strip or magnetic tape. Coupling means 183 are provided between the cable measuring device 116 and the recorder 182 so as to record at a speed which is a function of the speed of the logging cable 2Q.

An output from the scale-of-two circuit `174 is also connected to a scale-of-two resetting circuit 134. The scale-of-two resetting circuit 184 comprises a cathode follower 166 having its control grid connected to an output of the scale-of-two circuit 174i, its anode connected directly to the B+ supply and its cathode connected to a B- supply through a series combination of a first cathode resistor 199 and a second cathode resistor 192. A first capacitor 19d is connected at one terminal to ground and at the other terminal -to the common point between the iirst and second cathode resistors 1%', 192 through a first resistor 196 having a high resistance value. The common point between the first capacitor 194 and the high resistor 196 is connected to a control grid of a thyratron i955. A second resistor ZllZ, also having a high resistance value, is connected between the anode of the thyratron 19S and the B+ supply. An output transformer 204 has a primary winding 266 rwhich is connected at one terminal to ground and at the other terminal to the anode of the thyratron 198 through a second capacitor 2&8. The secondary winding 21d of the output transformer Ztl has one Iterminal connected to ground and the other terminal connected to the input of the scale-of-two circuit 174. A damping resistor 212 is connected across the secondary winding 210 of the transformer 284i.

FlG. 3 is a time sequence diagram illustrating the voltages produced at the output of the portion of the exploring unit and of the surface equipment indicated therein so as to facilitate the understanding of the operation of the acoustical velocity well logging system of the present invention.

ln operation, an electric pulse to produced by the timer unit 36 is applied to the acoustic transmitter pulser 38 which produces a sharp high energy electrical pulse for actuating the transmitting transducer 23 to generate an acoustic pulse To. In practice the transmitting transducer 23 generates an acoustic wave train rather than a single acoustic pulse since mechanical oscillations are produced in `the transmitting transducer 23 each time an electric pulse to from the acoustic transmitter pulse 3S is applied thereto. When theacoustic wave train arrives at one of the receiving transducers Sil, 32, the receivin7 transducer produces a corresponding electrical wave train at its output. Since only the first wave of the electrical wave train is used to measure the travel time of the acoustic energy to the borehole power supply 108 through the inductor 111i. The inductor 114 and the capacitor 112 are provided to prevent the pulses t1 and t2 from entering into the borehole power supply 16S. The voltage of the 60 cycle power supply 126 is, preferably, 280 volts so as to provide 240 volts at the input of the borehole power supply '198, since it has been found that a 4G volt drop exists in the cable 2t). However, as understood by those skilled in the art this voltage may be varied depending upon the circuits or elements used in the acoustic well logging system. The surface power supply L3, which is also energized by the 6G cycle per second, llO volt power source 125, supplies the B+, B-, negative direct current or bias voltage and filament voltage to the surface equipment. Since the surface power supply may also be a conventional power supply, details thereof have not been disclosed. With the elements of the system illustrated having the values indicated in the drawing, the B-ivoltage was 2.10 volts, the B- voltage was 105 volts and the negative direct current or bias voltage in the exploring unit was l volts and the negative direct current or bias voltage in the surface unit was 25 volts. it should be understood the units of the capacitance values of the capacitors illustrated in the drawing are microfarads.

The 60 cycle per second voltage from the power supply 12.6 is applied to the single conductor 22 of the single conductor cable Ztl through the inductor 124, the second primary winding 122 and then the iirst primary winding 1S of the transformer 12). The rst and second primary windings 118 and 122 are so wound that the linx changes due to the 60 cycle current in one primary vinding are cancelled by that in the other primary winding to produce a zero resultant 60 c.p.s. voltage in the secondary winding 134i.

The two pulses t1 and t2 applied to the lower end of the single conductor cable arrive at the upper end of the cable 2li displaced in time by an amount equal to the time delay in transmission through the single conductor cable 2t), which depends upon the transmission characteristics of the cable 2G. Since the electric pulses received at the earths surface are displaced in time they will be distinguished from the electric pulses l1 and t2 present in the exploring unit 13 by referring to the corresponding electric pulses at the earths surface as pulses 'l and 'g.

The pulse transmission time delay may be in the order of 5) microseconds for an 18,000 to 20,000 foot cable. However, since each of the two pulses are transmitted by the same conductor in the cable Ztl they are delayet by the same amount. Therefore, the time interval 'oetween the pulses t1 and l2 is the same as that between t1 and tz.

The two electric pulses fl and f2 received at the upper end of the single conductor cable 2@ are applied to one terminal of the rst primary winding 118 of the transformer 12- which is connected to ground at its other terminal by the capacitors 132 and 13? so as to prevent the pulses tl and t2 from passing through the second primary winding 122. Also, the inductor 124 is connected in series with the primary winding 122 to provide a high impedance to the pulses tl and t2 to further prevent them from passing through the second primary winding 122 of the transformer 129. The transformer 12@ acts as a stepup transformer so as to provide electric pulses tl and tg of sufiicient amplitude after passing through the high-pass filter 136 and the amplifier 13S to actuate the blocking oscillator 14o which produces at the output thereof sharp pulses of equal amplitude. The two pulses tl and tz from the blocking oscillator 140 are applied to the control grid of the cathode follower 176 to produce the pulses tl and :'2 across the cathode resistor 172 of the cathode follower 17d.

The pulses tl and f2 from the cathode of the cathode follower 171i are applied to the acoustical velocity logging systems time measuring circuit which includes tli scale-of-two circuit 174, the sawtooth generator 176, the peak reading vacuum tube voltmeter 178, the direct current voltage amplifier 186 and the recorder 182. The pulse tl when applied to the scale-of-two circuit 174 initiates a negative Wave or pulse at the output thereof which is terminated by the arrival of the pulse t'z. Accordingly, it can be seen that the duration of the negative pulse is equal to the time of travel of the acoustic wave through the subsurface formation between the first and second receiving transducers 3i) and 32. In order to conveniently measure the duration of the negative pulse from the scale-of-two circuit 174, the negative pulse is applied to the sawtooth generator 176, which produces a linearly increasing wave which continuously has a magnitude which is proportional to the time of travel of an acoustic pulse from the first receiving transducer 3@ to the second receiving transducer 32. Since the sawtooth lgenerator 176 is sharply cut olf at time f2, the peak value or" the sawtooth voltage produced at the output of the generator 176 is proportional to the total time of travel of the acoustic pulse through the subsurface formations between the iii-st and second receiving transducers 3o and 32. The peak value of the sawtooth voltage from generator 1763 is detected by the peak reading vacuum tube voltrneter 17S and applied to the recorder 182 through th direct current voltage amplilier 18@ to provide a record of the acoustic velocity through a portion of a subsurface formation. Since the transmitting transducer 28 is producing acoustic pulses To at a repetition rate of about 2C pulses per second, an accurate log of the acoustical velocities in substantially all subsurface formations traversed by a borehole may be obtained by moving the exploring unit 18 through the borehole.

Since the scale-of-two circuit 174 is a bi-stable circuit, it is necessary, in order to apply a pulse of the proper polarity to the sawtooth generator 176 to licasure the desired time intervals, to supply an even number of pulses to the input of the scale-of-'two circuit 174. It can be seen that if the pulse tl initiates the negative going pulse from the output of the scale-of-two circuit 174 but the pulse f2 fails to arrive at the input of the scaleoftwo circuit, the negative pulse will have a very long duration terminated only by the subsequent tl pulse. Thus, when the subsequent t2 pulse arrives, a positive pulse will be produced having a duration equal to the time of travel of the acoustic pulse through thc subsurface formations between the first and second receiving transducers. The sawtooth generator 176 would, of course, be responsive to the long negative pulse rather than tothe positive puise which now is equal to the desired time interval. This condition would persist u l an odd pulse would arrive to reset the scale-oftwo circuit so as to provide an output pulse of the proper polarity.

in accordance with an important feature of this invcntion, the scale-of-two resetting circuit 184 is provided to supply an artificial pulse t2 at an instant of time shortly after the passage of a tirneinterval during which a pulse 12 from the second transducer was expected but did not arrive at the scale-of-two circuit. in order to accomplish this result, a positive square wave or pulse initiated at the time ll at another output of the scale-of-two circuit 174 is applied to the control grid of the second cathode follower 135. The voltage developed across the second of the two series connected cathode resistors 192 is applied to the capacitor 194 through the high resistor 196. Tie voltage across the capacitor 194 thus increases gradually as shown at T n lil-G. 3 of the drawing. The trigger or tiring voltage Vt of the thyratron 1218 is set at a value which will be greater than the value of the voltage developed across the capacitor 19d during the time interval between pulses ll and f2. However, if the pulse tl or t2 does not arrive at the scale-of-two circuit 174, the voltage across the capacitor 174 will continue to increase until it reaches the trigger voltage Vt of the thyratron 1%. When this voltage Vt is attained, the thyratron will fire, discharging the energy stored in capacitor Zfli through the primary winding 2do of the transformer Zfifiand, once fired, will extinguish due to the high resistance value of the second resistor 202. The secondary winding 21) Will then apply the pulse t2 to the input of the scale-of-two circuit 174 to reset the circuit for the next cycle. Since the time duration between the pulses t1 and tz is a small portion of a cycle, that is, the time interval between two successively transmitted acoustic pulses T an extraneous pulse triggering the scale-of-two circuit also will not adversely affect the circuit to any great extent since the scale-of-two resetting circuit 134 will generally have time to operate to properly set the scale-oftwo circuit 174 for the next cycle of operation.

FIG. 4 of the drawing illustrates another embodiment of a cable pulsing circuit which may be used in the acoustical velocity system of the present invention. The circuit illustrated in FiG. 4 utilizes a semi-conductor device comprising a three-terminal solid-state thyratron of the type described in an article entitled Soiid-State Thyratrons Available Today, by T. P. Sylvan, in the March 6, 1959, issue of Electronics, pages 50 and 5l, and more particularly, a silicon controlled rectifier 214 having its anode connected to the pulse forming or storage network 94 and its cathode connected to the low cathode resistor fdd. The pulses t1 and t2 are applied from the cathodes of the dual cathode follower 56, illustrated also in FIG. 1 of the drawing, to the control element of the silicon controlled rectier 214 through a coupling transformer 216. The primary winding 218 of the transformer 216 is connected between the cathodes of the dual cathode follower 56 and ground. The secondary winding 22@ of the coupling transformer 216 is connected between the control element of the silicon controlled rectifier 2id and a negative direct current or bias potential. The silicon controlled rectifier 214 is, preferably, of the General Electric type ZJ 39-A-250 or C35H which performs as a fast acting switch in a manner similar to the hydrogen thyratron 88 illustrated in FIG. 1. An advantage of using the silicon controlled rectifier is that due to the lack of a filament therein, there is a considerable reduction in the required power for the silicon controlled rectifier without sacrificing the amount of energy transferred through the single conductor cable 2) to the surface equipment.

Although a two receiver acoustical system has been illustrated and described it should be understood that the present invention is not limited thereto. Other systems, for example, a single receiver acoustical system could be used wherein time measurements would be made between the electric pulses to and t1.

Accordingly, it can be seen that an improved acoustical velocity logging system has been provided which produces high quality acoustical velocity logs with the use of a transmission circuit which utilizes only one conductor to convey all electric energy between the surface equipment and the borehole or exploring unit.. Furthermore, the system transmits up the borehole the information desired from the two receiving transducers over a single conductor cable or transmission line while supplying the necessary operating energy from the earths surface to the exploring unit through the same single conductor cable or transmission line. The system of this invention provides an exploring unit which is relatively light in Weight yet supplies very accurate acoustic velocity logging information to the earths surface where it is converted into a form which can be readily recorded and studied.

Obviously, many modifications and variations of theI invention as hereinabove set forth, may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claims.

l ciaim:

l. An acoustical velocity well logging system comprising an elongated tooi adapted to be passed through the bore of a well, said tool having first and second transducers positioned in fixed spaced apart relationship in said tool, means for transmitting acoustic pulses at predetermined time intervals through a subsurface formation between said first and second transducers, said first and second transducers being in acoustic communication with said subsurface formation, means for producing a first electric pulse at the occurrence of a given one of said acoustic pulses at said first transducer, means for producing a second electric pulse upon the arrival of said given acoustic pulse at said second transducer, means defining a single conductor cable system, means operatively coupied and responsive to said means for producing said first and second electric pulses for transmitting said first and second electric pulses through the bore of the well in said single conductor system and a time measuring circuit disposed at the earths surface and operatively coupled to said means defining said single conductor cable system for measuring the time interval between said first and second electric pulses said means for transmitting said first and second electric pulses comprising a cable pulsing circuit including a thyratron having an output circuit coupied to said cable for applying high-power, short-duration pulses to said single conductor system and a pulse collecting circuit having a single output coupled to the input of said thyratron device and first and second input circuits, one of said pulse collecting input circuits being operatively coupled and responsive to the means for producing the rst electric pulse, and the second of said pulse collecting input circuits being operatively coupled and responsive to said means for producing said second electric pulse.

2. An acoustical velocity well logging system comprising an elongated tool adapted to be passed through a bore of a well, said tool having first and second transducers positioned in xed spaced apart relationship in said tool, means for transmitting acoustic pulses at predetermined time intervals through a subsurface formation between said first and second transducers, said first and second transducers being in acoustic communication with said subsurface formation, means for producing a first electric pulse at the occurrence of a given one of said acoustic pulses at said first transducer, means for producing a second electric pulse upon the arrival of said given acoustic pulse at said second transducer, a pair of electricaiiy conductive wires, means operatively coupled to said means for producing said first and second electric pulses and responsive to said first and second electric pulses for producing high-power, short-duration pulses, means for applying said high-power, short duration pulses to one end of said pair of wires and a time measuring circuit disposed at a remote point from said elongated tool and connected to the opposite end of said pair of wires for measuring the time interval between said first and second electric pulses, said means for producing high-power, short duration pulses comprising a thyratron device and a pulse collecting circuit having a unitary output coupled to an input of said thyratron device, said pulse collecting circuit comprising a circuit device having a common output circuit and first and second controlling input circuits, one of said controlling input circuits being operatively coupled to the means for producing said first electric pulse and the other of said controlling input circuits being operatively coupled to the means for producing said second electric pulse.

3. An acoustical velocity well logging system comprising an elongated tool adapted to be passed through the bore of a well, said tool having first and second transducers positioned in fixed spaced apart relationship in said tool, means for transmitting an acoustic pulse at predetermined time intervals through a subsurface formation between said first and second transducers, said first and second transducers being in acoustic communication ith said subsurface formation, means for producing a first electric pulse at the occurrence of a given one of said acoustic pulses at said first transducer, means for producing a second electric pulse upon the arrival of said given acoustic pulse at said second transducer, a single transmission line, means comprising, a cable pulsing circuit operatively coupled to said means for producing said first and second electric pulses and responsive to each of said first and second electric pulses for applying high-power, short duration pulses to one end of said transmission line, said cable pulsing circuit including a pulse forming network and a fast acting switch and a time measuring circuit disposed at a remote point from said elongated tool and connected to the other end of said single transmission line for measuring the time interval between said first and second electric pulses said cable pulsing circuit being operatively coupled to said means for producing said first and second electric pulses by means of a pulse collecting circuit, said pulse collecting circuit having a first input operatively coupled to the means for producing said first electric pulse and a second input operatively coupled to the means for producing said second electric pulse and an output operatively coupled to said fast acting swit n 4. An acoustical velocity well logging system comprising an elongated tool adapted to be passed through the bore of a well, said tool having first and second transducers positioned in fixed spaced apart relationship in said tool, means for transmitting an acoustic pulse at predetermined time intervals through a subsurface formation between said first and second transducers, said first and second transducers being in acoustic communication With said subsurface formation, means for producing a first electric pulse at the occurrence of a given one of said acoustic pulse at said first transducer, means for producing a second electric pulse upon the arrival of said given acoustic pulse at said second transducer, a single transmission line, a first normally inoperable trigger generator including a gas tube having at least a pair of control grids, said rst trigger generator including an input and an output, said first trigger generator input comprising said pair of first trigger generator gas tube control grids means for applying said first electric pulse to one of said control grids, a first rate generator adapted to produce a pulse during at least a time interval when said first electric pulse is expected to be produced by said first pulse producing means, said first gate generator having an input including said pair of second trigger generator gas tube control grids and an output, the output of said first gate generator being connected to the other control grid of said gas tube, a cable pulsing circuit for applying highpower, short duration pulses to said single transmission line, said cable pulsing circuit including an input and an output, means for coupling the output from said first trigger generator to the input of said cable pulsing circuit, a second normally inoperable trigger generator including a gas tube having at least a pair of control grids, said second trigger generator including an input and an output, said second trigger generator input including said pair of second trigger generator gas tube control grids, means for applying the second electric pulse to one of said pair of control grids, a second gate generator adapted to produce a pulse during at least a time interval when said second electric pulse is expected to be produced by said second pulse producing means, said second gate generator having an input and an output, and means including the output of said second trigger generator for applying a signal to the input of said second gate generator at the appropriate time to produce a pulse at the output of Said generator during at least a time interval when said second electric pulse is expected to be produced by said second pulse producing means, the output from said second gate generator being applied to the other of said pair or control grids of said gas tube of said second trigger generator, means for coupling the output from said second trigger generator to the input of said cable pulsing circuit and a time measuring circuit disposed at a remote point from said elongated tool and connected to the other end l2 of said single transmission line for measuring the time interval between said first and second electric pulses.

5. An acoustical velocity well logging system comprising an elongated tool adapted to be passed through the bore of a well, said tool lhaving first and second transducers positioned in fixed spaced apart relationship in said tool, means for transmitting an acoustic pulse at predetermined time intervals through a subsurface formation between said first and second transducers, said first and second transducers being in acoustic communication with said subsurface formation, means for producing a first electric pulse at the occurrence of a given one of said acoustic pulses at said first transducer, means for producing a second electric pulse upon the arrival of said given acoustic pulse at said second transducer, a single transmission line, a cable pulsing circuit for applying high-power, short-duration pulses to one end of said transmission line, said cable pulsing circuit including an input and an output, the output of said cable pulsing circuit being coupled to said one end of said transmission line, a pulse collecting circuit including a dual Cathode follower having two control grids, said pulse collecting circuit including an input and an output, the input of said pulse collecting circuit including said two control grids of said pulse collecting circuit dual cathode means for applying said first electric pulse to one of said control grids, means for applying said second electric pulse to the other of said control grids, means for applying the output from said pulse collecting circuit to the input of said cable pulsing circuit and a time measuring circuit disposed at a remote point from said elongated tool and connected to the other end of said single transmission line for measuring the time interval between said first and second electric pulses.

6. An acoustical velocity Well logging system comprising an elongated tool adapted to be passed through the bore in a well, said tool having an acoustical transmitting transducer `and first and second receiving tuansducers, said transducers being positioned in longitudinally fixed spaced apart relationship in said tool, means coupled to said transmitting transducers for producing an acoustic pulse at predetermined time intervals for passage through a subsurface formation between said first and second receiving transducers, said transmitting transducer and said first and second receiving transducers being in acoustic communication with said subsurface formation, means for producing a first electric pulse upon the arrival of a given one of said acoustic pulses at said first receiving transducers, means for producing a second electric pulse upon the arrival of said given acoustic pulse at said second receiving transducer, a single conductor cable, a first normally inoperable trigger generator including a gas tube having two control grids, said first trigger generator including an input and an output, said first trigger generator input including said two first trigger generator gas tube control grids, means for applying said first electric pulse to one of said rst trigger generator control grids, a first pulse delay unit including an input and an output, said first pulse delay unit input being coupled to said means for producing an acoustic pulse, a first gate generator having an input and an output, said first gate generator input being coupled to said first pulse delay unit said first gate generator output being coupled to the other control grid of said first trigger generator gas tube, said first pulse delay unit and said first generator being adapted to apply a voltage to said other control grid of said gas tube during at least a timerinterval when-an electric pulse from said first receiving transducer is expected, a pulse collecting circuit including a dual cathode follower having two grids, said pulse collecting circuit including an input and an output, the input of said pulse collecting circuit including said two pulse collecting circuit cathode follower grids, means for coupling the output from said first trigger generator to one of the control grids of said dual cathode follower, a cable pulsing circuit including a pulse forming network and a hydrogen thyratron, said thyratron having an input circuit including a control grid and an Output circuit coupled to said pulse forming network and to one end of said single conductor cable to apply energy to said one end of said single conductor cable, means for coupling the output of said pulse collecting circuit to the control grid of said hydrogen thyratron, a second normally inoperable trigger generator including a gas tube having two control grids, said second trigger .generator having an input and an output, said second trigger generator output including the two control grids of said second trigger generator gas tube means for applying said second electric pulse to one of the control grids of the gas tube of said second trigger generator, a second pulse delay unit coupled to the output of said first trigger generator, a second gate generator having an input and an output, said second gate generator input being coupled to the output of said second pulse delay unit, said second gate generator output being coupled to the other of the tWo control grids of the gas tube of said second trigger generator, said second pulse delay unit and said second gate generator being adapted to apply a Voltage to the other of the two control grids of' said second generator during at least a time interval when an electric pulse from said second receiving transducer is expected, means for coupling the output of said second trigger generator to the other control grid of said dual cathode follower and a time measuring circuit disposed at a remote point from said elongated tool and connected to the other end o-f said single conductor cable for measuring the time interval between said first and second electric pulses.

7. An acoustical velocity well logging system comprising an elongated tool adapted to be passed through the bore of a well, said tool having first and second transducers positioned in fixed spaced apart relationship in said tool, means for transmitting an acoustic pulse at predetermined time yintervals through a subsurface formation between said first and second transducers, said first and second transducers being in acoustic'communication with said subsurface formation, means for producing a first electric pulse at the occurrence of a given one of said acoustic pulses at said first transducer, means for producing a second electric pulse upon the arrival of said given acoustic pulse at said second transducer, a single transmission line, means for applying said first and second electric pulses to a -first point on said transmission line, and a time measuring device including a scale-oftwo circuit disposed at a remote point from said elongated tool and connected to the other end of said single transmission line, said system further including means operatively coupled to said other end of said single transmission line for controlling the duration of a pulse of given polarity produced by said scale-of-two circuit as a function of the time interval between said first and second electric pulses, and means for measuring the duration of said pulse produced by said scale-oftwo circuit as an indication of the time interval between said first and second electric pulses.

8. An acoustical velocity well logging system cornprising an elongated tool adapted to be passed through the bore of a well, said tool having first and second transducers positioned in fixed spaced apart relationship in said tool, means for transmitting an acoustic pulse at predetermined time intervals through a subsurface formation between said first and second transducers, said first and second transducers being in acoustic communication with said subsurface formation, means for producing a first electric pulse at the occurrence of a given one of said acoustic pulses at said first transducer, means for producing a second electric pulse upon the arrival of said given acoustic pulse at said second transducer, a single transmission line, means Vfor applying said first and second electric pulses to one end of said single transmission line, a time measuring device including a scale-of-two circuit responsive to said first and second electric pulses, said time measuring device being disposed at a remote point from said elongated tool and connected to the other end of said single transmission line for measuring the time interval between said first and second electric pulses, means coupled to an output of said scale-of-two circuit for applying a pulse to the input of said scale-of-two circuit in the event that one of said first and second electric pulses does not actuate said scale-of-two circuit.

9. An acoustical velocity Well logging system comprising an elongated tool adapted to be passed through the bore of a Well, said tool having first and second transducers positioned in fixed spaced apart relationship in said tool, means for transmitting an acoustic pulse at predetermined time intervals through a subsurface formation between said first and second transducers, said first and second transducers being in acoustic communication with said subsurface Iformation, means for producing a first electric pulse at the occurrence of a given one of said acoustic pulses at said first transducer, means for producing a second electric pulse upon the arrival of said given acoustic pulse at said second transducer, a single transmission line, means for applying said first and second electric pulses to one end of said single transmission line, a time measuring device including a scale-of-two circuit disposed at a remote point from said elongated tool and connected to the opposite end of said single transmission line for measuring the time interval between said first and second electric pulses and a scale-of-two resetting circuit including a gas tube having a control grid and adapted to be triggered by a voltage of a predetermined value and means responsive to an output signal from said scale-of-two circuit and coupled to said control grid for producing a unidirectionally varying voltage having a range of values including said predetermined value, the output of said scale-of-two resetting circuit being coupled to the input of said scale-of-two` circuit.

10. An acoustical velocity well logging system comprising an elongated tool adapted to be passed through a borehole of the Well, said tool having first and second transducers positioned in fixed spaced apart relationship in said tool, means for transmitting acoustical pulses at predetermined time intervals through a sulbsurface formation between said first and second transducers, said first and second transducers being in acoustic communication with said subsurface formation, means for producing a first electric pulse at the occurrence of a given one of said acoustical pulses at said first transducer, means for producing a second electric pulse upon the arrival ot' said given acoustic pulse at said second transducer, a single conductor cable, a cable pulsing circuit including a pulse forming network and a semi-conductor device, said cable pulsing circuit including an input operatively coupled and responsive to said first and second electric pulses Ifor applying energy from said pulse `forming network to one end of said single conductor cable, said cable pulsing circuit further comprising a pulse collecting circuit having a first input operatively coupled to the means for producing said first electric pulse, a second input circuit operatively coupled to the means for producing said second electric pulse and an output circuit for coupling the collected pulses to the input of said semi-conductor device and a time measuring circuit disposed at a remote point from said elongated tool and connected to the other end of said single conductor cable for measuring the time interval between said first and second electric pulses.

11. An acoustical velocity Well logging system as set forth in claim l() wherein said semi-conductor device is a three-terminal solid-state thyratron.

12. An acoustical velocity well logging system as set forth in claim l1 wherein said solid-state thyratron is a silicon controlled rectifier.

p1 la 13. A system for determining the acoustical velocity through a subsurface formation traversed by a borehoie comprising means for transmitting an acoustic pulse through the subsurface formation between first and second spaced apart points in the borehole, means for producing first and second electric pulses at the presence of said acoustic pulse at said first and second points, respectively, a single transmission line, means having a Common, lovI impedance output circuit for applying relatively high energy and short duration electric pulses corresponding to said first and second electric pulses to one end of said single transmission line, said pulsing means having an input circuit including a pulse collecting means for applying thereto said first and second electric pulses, and means coupled to the opposite end of said transmission line for measuring the time interval between said first and second electric pulses.

14. An acoustical velocity well logging system comprising an elongated tool adapted to be passed through the bore of the well, said tool having rst and second transducers positioned in fixed spaced apart relationship in said tool, means for transmitting an acoustic pulse at predetermined time intervals through a subsurface formation between said first and second transducers, said first and second transducers being in acoustic communication with said subsurface formation, means for producing a first electric pulse at the occurrence of a given one of said acoustic pulses at said first transducer, means for producing a second electric pulse upon the arrival of Said given acoustic pulse at said second transducer, a single transmission line, means operatively coupled to said means for producing said first and second electric pulses and responsive to said first and second electric pulses for producing high-power, shortduration pulses and for applying said high-power, short-duration pulses to one end of said transmission line, a time measuring circuit disposed at a remote point rom said elongated tool and connected to the opposite end of said transmission line for measuring the time interval between said rst and ser:v ond electric pulses, an electric power source, first filter means for connecting said power source to said opposite end of said transmission line and for separating said first and second electric pulses from the energy derived from said power source, means disposed at said one end of said second transmission line for receiving the energy from said power source and second filtering means operatively coupled between said energy receiving means and said single transmission line for preventing said lfirst and second electric pulses from entering said energy receiving means, said first filtering means including a transformer having first, second and third windings, an inductor having one terminal connected to said electrical power source, said first and second windings being serially connected between the other terminal of said inductor and said single transmission line, said first and second windings being so formed as to produce in said third winding a zero resultant voltage when energy from said power source is passing therethrough, a irst capacitor connected between said one terminal of said inductor and the common point between said first and second windings and a second capacitor connected between said one terminal of said inductor and ground, said third winding being coupled to the time measuring circuit, said tirst and second capacitors and said inductor having values so as to provide effectively a ground connection at the common point between said first and second windings for said rst and second electric pulses.

References Cited in the file of this patent UNlTED STATES PATENTS 2,651,027 Vogel Sept. l, 1953 2,708,485 Vogel May 17, 1955 2,779,931 Hersey Jan. 29, 1957 2,931,455 Loofbourrow Apr. 5, 1960 2,938,592 Charske et al May 3,1, 19610 3,618,839 Isaacson Jan. 30,l 1962 

1. AN ACOUSTICAL VELOCITY WELL LOGGING SYSTEM COMPRISING AN ELONGATED TOOL ADAPTED TO BE PASSED THROUGH THE BORE OF A WELL, SAID TOOL HAVING FIRST AND SECOND TRANSDUCERS POSITIONED IN FIXED SPACED APART RELATIONSHIP IN SAID TOOL, MEANS FOR TRANSMITTING ACOUSTIC PULSES AT PREDETERMINED TIME INTERVALS THROUGH A SUBSURFACE FORMATION BETWEEN SAID FIRST AND SECOND TRANSDUCERS, SAID FIRST AND SECOND TRANSDUCERS BEING IN ACOUSTIC COMMUNICATION WITH SAID SUBSURFACE FORMATION, MEANS FOR PRODUCING A FIRST ELECTRIC PULSE AT THE OCCURRENCE OF A GIVEN ONE OF SAID ACOUSTIC PULSES AT SAID FIRST TRANSDUCER, MEANS FOR PRODUCING A SECOND ELECTRIC PULSE UPON THE ARRIVAL OF SAID GIVEN ACOUSTIC PULSE AT SAID SECOND TRANSDUCER, MEANS DEFINING A SINGLE CONDUCTOR CABLE SYSTEM, MEANS OPERATIVELY COUPLED AND RESPONSIVE TO SAID MEANS FOR PRODUCING SAID FIRST AND SECOND ELECTRIC PULSES FOR TRANSMITTING SAID FIRST AND SECOND ELECTRIC PULSES THROUGH THE BORE OF THE WELL IN SAID SINGLE CONDUCTOR SYSTEM AND A TIME MEASURING CIRCUIT DISPOSED AT THE EARTH''S SURFACE AND OPERATIVELY COUPLED TO SAID MEANS DEFINING SAID SINGLE CONDUCTOR CABLE SYSTEM FOR MEASURING THE TIME INTERVAL BETWEEN SAID FIRST AND SECOND ELECTRIC PULSES SAID MEANS FOR TRANSMITTING SAID FIRST AND SECOND ELECTRIC PULSES COMPRISING A CABLE PULSING CIRCUIT INCLUDING A THYRATRON HAVING AN OUTPUT CIRCUIT COUPLED TO SAID CABLE FOR APPLYING HIGH-POWER, SHORT-DURATION PULSES TO SAID SINGLE CONDUCTOR SYSTEM AND A PULSE COLLECTING CIRCUIT HAVING A SINGLE OUTPUT COUPLED TO THE INPUT OF SAID THYRATRON DEVICE AND FIRST AND SECOND INPUT CIRCUITS, ONE OF SAID PULSE COLLECTING INPUT CIRCUITS BEING OPERATIVELY COUPLED AND RESPONSIVE TO THE MEANS FOR PRODUCING THE FIRST ELECTRIC PULSE, AND THE SECOND OF SAID PULSE COLLECTING INPUT CIRCUITS BEING OPERATIVELY COUPLED AND RESPONSIVE TO SAID MEANS FOR PRODUCING SAID SECOND ELECTRIC PULSE. 